Manifest Destiny

the belief or doctrine, held chiefly in the middle and latter part of the 19th century, that it was the destiny of the U.S. to expand its territory over the whole of North America and to extend and enhance its political, social, and economic influences.

manifest destiny definition

A popular slogan of the 1840s. It was used by people who believed that the United States was destined — by God, some said — to expand across North America to the Pacific Ocean. The idea of manifest destiny was used to justify the acquisition of Oregon and large parts of the Southwest, including California. (SeeMexican War.)